If I'm going to replace my supercharger (at 125k mi I think it's about time to start thinking about it) ... do I want a rebuilt one or a new one?

I found this place: http://www.superchargertech.com ... $500 rebuilt ... this is the best price I've seen yet.

New MB Genuine units seem to be going for ~$1000-1100 online.

Suggestions?

Thanks. John

I disagree with the first part of your post. Unless your supercharger has a particular problem you do not really have to start thinking about replacing it at any mileage...it's not a mileage dependent wear item. Many cars go north of 250k with original supercharger.
If you still want to replace yours, consider having it rebuilt at a specialty shop or buying a reman. I'm willing to bet that even those new MB units are actually re manufactured to a certain extent

RWDlifer is correct - the S/C isn't a mileage dependent item. I wouldn't replace it unless you are having issues.

I bought a new one on ebay for $600 some years ago.
Sold the old one for $250. Also at about 125K miles.
Did the alternator too. Had it rebuilt by an auto electrics place..
Better than waiting for it to fail far from home.
DIY neither are expensive repairs, and good insurance to in advance along with the alternator.
Non-diy far from home, could cost thousand$.
For me at 125K, I did the SC, alternator, belts, flushed the tranny, diff oil,
fuel filter, coolant, brake fluid. Wished I'd done the starter too since it went 20K miles later.
If you do all that, you won't have much to worry about for a long time.
Likely you won't find a new one these days.
Just find an old one and having it rebuilt.

good points. also consider the cost of labor if you arent planning on doing it yourself. even an indy will charge several hours for removal and replace.

The price is ok. Its not an easy DIY task. I replaced the bearings by my own and it was several evenings of work just for preparing all tools you need. Hydraulic press, pressure plates and steel tubes and so on
Example (not me)

From my little experience, I had three M45 in my hand, I found at least one fault at a mileage of 100k. One problem is that Mercedes doesn't do an oil change/refill.

If you want to drive the car for some more years, I would recommend to do a rebuild. BTW: You need to replace the belt tensioner also to minimize belt slip, buy a Litens part.

Over 290K miles on mine, and still gives good boost. I have gone through two tensioners though. If you are inclined to go through with a replacement, I would get a rebuilt unit.